Stevie Nicks almost helped write Purple Rain. The singer has revealed that Prince asked her to write lyrics for what is now one of his most famous songs. "It was so overwhelming," she said in a recent interview. "I just got scared."

Nicks and Prince have been friends for decades. But they didn't collaborate until 1983, when Nicks found herself humming along to Little Red Corvette while she was driving through Los Angeles. She pulled over, scrawling some lyrics to accompany the melody – and then rang up Price.

"Don't even ask me how I found his number but I did," she told the Minneapolis Star Tribune. "I told him: 'I'm recording this song and I wrote it to Little Red Corvette and I'm giving you 50% of it and I want to know if you'd like to come play [synthesisers] on it on one of the next three nights.' He was there in an hour. And we became friends."

That song became Stand Back, which appeared on Nicks's solo album The Wild Heart. Although Prince's performance is uncredited, the writing credit was probably worth millions – Stand Back was a huge hit.

But the prospect of an even bigger collaboration came when Prince sent over a cassette of music he was working on. It included a long instrumental track, which needed words. "It was so overwhelming, that 10-minute track … I listened to it and I just got scared," Nicks said. "I called him back and said, 'I can't do it. I wish I could. It's too much for me.' I'm so glad that I didn't, because he wrote it, and it became Purple Rain."

Prince's subsequent LP, 1984's Purple Rain, has sold more than 20m copies worldwide.